The state of the art as concerns the manufacture of long life high current density cathodes involves the initial mixing and heating of barium carbonate, BaCO.sub.3 calcium carbonate, CaCO.sub.3 and aluminum oxide, Al.sub.2 O.sub.3. The BaCO.sub.3 and CaCO.sub.3 are decomposed at 1450.degree. C. to form BaO and CaO which react with the Al.sub.2 O.sub.3 to form aluminates. The aluminates are then impregnated into a porous billet of tungsten or tungsten and iridium or tungsten and osmium, or tungsten and rhodium, etc. heated in a cathode environment, and testing made. The process involves the decomposition of the aluminates to form the barium iridiates, barium osmiates and barium rhodiates.